As an inkjet printer, in recent years, an inkjet printer including a recording head provided with nozzles for jetting ink, which is cured by being irradiated with an ultraviolet ray, and an ultraviolet ray irradiation device radiating the ultraviolet ray to cure the ink has been used.
Here, if a time after the ink has landed on a recording medium till the ultraviolet ray is radiated thereon is long, the diameter of the dot of the ink which has landed on the recording medium is expanded. Then, the generation of a blur and a mixture of colors arise to lower an image quality. Accordingly, in order to shorten the time after the ink has landed on the recording medium till the ultraviolet ray is radiated, in a conventional inkjet printer, the ultraviolet ray irradiation device equipped with a cover member covering a light source is provided in close vicinity to the recording head (JP-Tokukaisyou-60-132767: hereinafter referred to as Patent Document 1).
However, in the conventional inkjet printer (Patent Document 1), some ultraviolet rays radiated from the ultraviolet ray light source are reflected on the inner surface of the cover member covering the light source, the surface of the recording medium and the like, and the reflected ultraviolet rays have reached the recording head. For example, as shown in FIG. 17, as for an ultraviolet ray which has radiated from an ultraviolet ray light source 15 and has been reflected on a surface of a cover member 16 which is perpendicular to a recording medium 17, an incident angle R thereof to the surface of the recording medium 17 is large, and a reflection angle r thereof on the surface of the recording medium 17 is also large. Consequently, it is easy for the reflected ultraviolet ray to pass through a space between the cover member 16 and the recording medium 17 to enter a recording head 6.
In this case, there is the following problem. That is, the ultraviolet ray is radiated on the ink adhering to a nozzle surface, which is a surface on which the nozzle of the recording head is provided, and on the ink in the nozzle, and consequently the ink is bodied or cured to generate imperfect jetting. In particular, as the ink to be cured by the ultraviolet ray, there are known a radical polymerization series ink and a cationic polymerization series ink. Among them, since the cationic polymerization series ink does not receive the inhibition of polymerization by oxygen, which the radical polymerization series ink receives, the sensitivity of the cationic polymerization series ink is high, and also the cationic polymerization series ink has a property of the acids belonging to active species of accumulating light energy. Consequently, when the ultraviolet ray is radiated on the ink adhering on the nozzle surface or on the ink in the nozzle in a case of using the cationic polymerization series ink, the imperfect jetting of the ink is easy to be produced.